U.S. patent number 10,096,292 [Application Number 15/054,235] was granted by the patent office on 2018-10-09 for liquid crystal display systems and related methods with pixel elements driven at different frequencies.
This patent grant is currently assigned to A.U. VISTA INC., THE UNIVERSITY OF CENTRAL FLORIDA RESEARCH FOUNDATION, INC.. The grantee listed for this patent is a.u. Vista Inc.. Invention is credited to Hai-Wei Chen, Yi-Fen Lan, Cheng-Yeh Tsai, Shin-Tson Wu.
United States Patent |
10,096,292 |
Chen , et al. |
October 9, 2018 |
Liquid crystal display systems and related methods with pixel
elements driven at different frequencies
Abstract
Liquid crystal display (LCD) systems and related methods with
pixel elements driven at different frequencies are provided. A
representative LCD system includes: a plurality of pixel elements
arranged in an array, each of the plurality of pixel elements
having a first sub-region and a second sub-region; a low-frequency
driving circuit operative to drive each of the first sub-regions;
and a high-frequency driving circuit operative to drive each of the
second sub-regions at a driving frequency different than a driving
frequency of the low-frequency driving circuits; wherein the first
sub-regions exhibit a different size than the second
sub-regions.
Inventors: |
Chen; Hai-Wei (Orlando, FL),
Wu; Shin-Tson (Orlando, FL), Lan; Yi-Fen (Taichung,
TW), Tsai; Cheng-Yeh (Hsinchu, TW) |
Applicant: |
Name |
City |
State |
Country |
Type |
a.u. Vista Inc. |
Milpitas |
CA |
US |
|
|
Assignee: |
A.U. VISTA INC. (Milpitas,
CA)
THE UNIVERSITY OF CENTRAL FLORIDA RESEARCH FOUNDATION, INC.
(Orlando, FL)
|
Family
ID: |
59679699 |
Appl.
No.: |
15/054,235 |
Filed: |
February 26, 2016 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
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US 20170249917 A1 |
Aug 31, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G09G
3/3648 (20130101); G09G 3/3614 (20130101); G02F
2001/13793 (20130101); G09G 2340/0435 (20130101); G09G
2320/041 (20130101) |
Current International
Class: |
G09G
3/36 (20060101); G02F 1/1343 (20060101); G02F
1/137 (20060101) |
Field of
Search: |
;345/87-102,204-214 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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201007318 |
|
Feb 2010 |
|
TW |
|
201407247 |
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Feb 2014 |
|
TW |
|
Other References
English Translation of TW 201007318. cited by examiner.
|
Primary Examiner: Zhou; Hong
Attorney, Agent or Firm: McClure, Qualey & Rodack,
LLP
Claims
What is claimed is:
1. A liquid crystal display (LCD) system comprising: a plurality of
pixel elements arranged in an array, each of the plurality of pixel
elements having a first sub-region and a second sub-region; a
low-frequency driving circuit operative to drive each of the first
sub-regions; a high-frequency driving circuit operative to drive
each of the second sub-regions at a driving frequency different
than a driving frequency of the low-frequency driving circuits; the
plurality of pixel elements having a plurality of first electrodes
associated with the first sub-regions and a plurality of second
electrodes associated with the second sub-regions; a first
substrate upon which the plurality of first electrodes are
disposed; a second substrate upon which the plurality of second
electrodes are disposed; and a blue phase liquid crystal material
disposed between the first substrate and the second substrate for
forming the plurality of pixel elements; wherein the low-frequency
driving circuit and the high-frequency driving circuit are
separately operative to drive the first sub-regions and the second
sub-regions simultaneously such that an operating voltage of the
plurality of pixel elements is lower than the operating voltage
associated with driving both the first sub-regions and the second
sub-regions at a low frequency corresponding to the low-frequency
driving circuit, and the operating voltage of the plurality of
pixel elements is lower than the operating voltage associated with
driving both the first sub-regions and the second sub-regions at a
high frequency corresponding to the high-frequency driving
circuit.
2. The LCD system of claim 1, wherein the first sub-regions are
smaller than the second sub-regions.
3. The LCD system of claim 1, wherein the driving frequency of the
high-frequency driving circuits is a multiple of the driving
frequency of the low-frequency driving circuits.
4. The LCD system of claim 1, wherein the plurality of first
electrodes exhibit a different configuration than the plurality of
second electrodes.
5. The LCD system of claim 4, wherein the first electrodes exhibit
gaps between adjacent ones of the first electrodes that are
narrower than gaps exhibited between adjacent ones of the second
electrodes.
6. The LCD system of claim 1, wherein a ratio of the size of the
first sub-region and the second sub-region is in the range of 1 to
approximately 10, but 1 is excluded.
7. The LCD system of claim 1, wherein each of the second
sub-regions is at least two times larger or smaller than each of
the first sub-regions.
8. The LCD system of claim 1, further comprising: a first data line
communicating with each of the low-frequency driving circuits; a
second data line communicating with each of the high-frequency
driving circuits; a first gate line communicating with each of the
low-frequency driving circuits; and a second gate line
communicating with each of the high-frequency driving circuits.
9. The LCD system of claim 8, wherein: each of the low-frequency
driving circuits has a first switch, coupled to the corresponding
first data line, with a first gate terminal coupled to the
corresponding first gate line; and each of the high-frequency
driving circuits has a second switch, coupled to the corresponding
second data line, with a second gate terminal coupled to the
corresponding second gate line.
10. The LCD system of claim 1, wherein the low frequency driving
circuit is configured to operate in a range of approximately 60 Hz
to approximately 120 Hz.
11. The LCD system of claim 1, wherein the high frequency driving
circuit is configured to operate in a range of approximately 120 Hz
to approximately 480 Hz.
12. The LCD system of claim 1, wherein the operating voltage of the
plurality of pixel elements associated with driving the first
sub-regions and the second sub-regions simultaneously is lower than
17.5 V for operating temperatures between approximately
0-40.degree. C.
13. A method of driving a liquid crystal display (LCD) comprising:
providing an LCD having a plurality of pixel elements arranged in
an array, a plurality of driving circuits configured to drive the
plurality of pixel elements, the plurality of pixel elements having
a plurality of first electrodes associated with corresponding first
sub-regions and a plurality of second electrodes associated with
corresponding second sub-regions, a first substrate upon which the
plurality of first electrodes are disposed, a second substrate upon
which the plurality of second electrodes are disposed, and a blue
phase liquid crystal material disposed between the first substrate
and the second substrate; driving the corresponding first
sub-region of each of the pixel elements at a first driving
frequency; and driving the corresponding second sub-region of each
of the pixel elements at a second driving frequency different than
the first driving frequency; wherein the low-frequency driving
circuit and the high-frequency driving circuit are separately
operative to drive the first sub-regions and the second sub-regions
simultaneously such that an operating voltage of the plurality of
pixel elements is lower than the operating voltage associated with
driving both the first sub-regions and the second sub-regions at
the first driving frequency, and the operating voltage of the
plurality of pixel elements is lower than the operating voltage
associated with driving both the first sub-regions and the second
sub-regions at the second driving frequency.
14. The method of claim 13, wherein the second driving frequency is
a multiple of the first driving frequency.
15. The method of claim 13, wherein the first driving frequency is
in a range of approximately 60 Hz to approximately 120 Hz.
16. The method of claim 13, wherein the second driving frequency is
in a range of approximately 120 Hz to approximately 480 Hz.
17. The method of claim 13, wherein the operating voltage of the
plurality of pixel elements associated with driving the first
sub-regions and the second sub-regions simultaneously is lower than
17.5 V for operating temperatures between approximately
0-40.degree. C.
18. An LCD system, comprising: a first substrate; a second
substrate; a blue phase liquid crystal material disposed between
the first substrate and the second substrate; a first electrode
disposed on the first substrate; a second electrode disposed on the
second substrate; a pixel element having a first sub-region and a
second sub-region; a low-frequency driving circuit disposed on the
first sub-region; a high-frequency driving circuit disposed on the
second sub-region; a plurality of date lines, with a first of the
date lines being coupled to the low-frequency driving circuit and a
second of the data lines being coupled to the high-frequency
driving circuit; and a plurality of gate lines, with a first of the
gate lines being coupled to the low-frequency driving circuit and a
second of the gate lines being coupled to the high-frequency
driving circuit; wherein the first electrode corresponds to the
first sub-region and is coupled to the low-frequency driving
circuit, and the second electrode corresponds to the second
sub-region and is coupled to the high-frequency driving circuit;
wherein the low-frequency driving circuit and the high-frequency
driving circuit are separately operative to drive the first
sub-region and the second sub-region simultaneously such that an
operating voltage of the pixel element is lower than the operating
voltage associated with driving both the first sub-region and the
second sub-region at a low frequency corresponding to the
low-frequency driving circuit, and the operating voltage of the
pixel element is lower than the operating voltage associated with
driving both the first sub-region and the second sub-region at a
high frequency corresponding to the high-frequency driving
circuit.
19. A liquid crystal display (LCD) system, comprising: a plurality
of pixel elements arranged in an array, each of the plurality of
pixel elements having a first sub-region and a second sub-region,
the plurality of pixel elements having a plurality of first
electrodes associated with corresponding first sub-regions and a
plurality of second electrodes associated with corresponding second
sub-regions; a first substrate upon which the plurality of first
electrodes are disposed; a second substrate upon which the
plurality of second electrodes are disposed; a blue phase liquid
crystal material disposed between the first substrate and the
second substrate; a first gate signal having a first driving
frequency; and a second gate signal having a second driving
frequency different from the first driving frequency; wherein the
first sub-regions are configured to receive the first gate signal
and the second sub-regions are configured to receive the second
gate signal simultaneously such that an operating voltage of the
plurality of pixel elements is lower than the operating voltage
associated with driving both the first sub-regions and the second
sub-regions at a low frequency corresponding to the low-frequency
driving circuit, and the operating voltage of the plurality of
pixel elements is lower than the operating voltage associated with
driving both the first sub-regions and the second sub-regions at a
high frequency corresponding to the high-frequency driving
circuit.
20. The LCD system of claim 19, further comprising: a first data
signal having the first driving frequency; and a second data signal
having the second driving frequency; wherein the first sub-region
is configured to receive the first data signal and the second
sub-region is configured to receive the second data signal
simultaneously.
21. The LCD system of claim 20, wherein the voltage (amplitude) of
the first data signal is substantially the same with the voltage
(amplitude) of the second data signal.
22. A liquid crystal display (LCD) system, comprising: a first
substrate having a plurality of first electrodes; a second
substrate having a plurality of second electrodes; a blue phase
liquid crystal layer disposed between the plurality of first
electrodes and the plurality of second electrodes; a plurality of
pixel elements arranged in an array, each of the plurality of pixel
elements having a first sub-region corresponding to one of the
plurality of the first electrodes and a second sub-region
corresponding to one of the plurality of the second electrodes; a
first gate signal having a first driving frequency; a second gate
signal having a second driving frequency different from the first
driving frequency; a first data signal having the first driving
frequency; and a second data signal having the second driving
frequency; wherein the first gate signal and the first data signal
are operative to drive the first sub-region, and the second gate
signal and the second data signal are operative to drive the second
sub-region such that an operating voltage of the plurality of pixel
elements is lower than the operating voltage associated with
driving both the first sub-region and the second sub-region at the
first driving frequency, and the operating voltage of the plurality
of pixel elements is lower than the operating voltage associated
with driving both the first sub-region and the second sub-region at
the second driving frequency.
23. The LCD system of claim 22, wherein the voltage (amplitude) of
the first data signal is substantially the same with the voltage
(amplitude) of the second data signal.
Description
BACKGROUND
Technical Field
The disclosure generally relates to liquid crystal displays.
Description of the Related Art
Liquid crystal displays (LCDs) are widely used in electronic
devices, such as laptops, smart phones, digital cameras,
billboard-type displays, and high-definition televisions.
LCD panels may be configured as disclosed, for example, in Wu et
al., U.S. Pat. No. 6,956,631, which is assigned to AU Optronics
Corp., the parent company of the assignee of the current
application, and hereby incorporated by reference in its entirety.
As disclosed in Wu et al. FIG. 1, the LCD panel may comprise a top
polarizer, a lower polarizer, a liquid crystal cell, and a back
light. Light from the back light passes through the lower
polarizer, through the liquid crystal cell, and then through the
top polarizer. As further disclosed in Wu et al. FIG. 1, the liquid
crystal cell may comprise a lower glass substrate and an upper
substrate containing color filters. A plurality of pixels
comprising thin film transistor (TFT) devices may be formed in an
array on the glass substrate, and a liquid crystal compound may be
filled into the space between the glass substrate and the color
filter forming a layer of liquid crystal material.
As explained in Sawasaki et al., U.S. Pat. No. 7,557,895, which is
assigned to AU Optronics Corp., the parent company of the assignee
of the current application, and hereby incorporated by reference in
its entirety, the thickness of the liquid crystal layer typically
must be uniformly controlled, in order to avoid unevenness in
brightness across the LCD panel. As disclosed in Sawasaki et al.,
the required uniformity may be achieved by disposing a plurality of
pillar spacers between the TFT substrate and the color filter
substrate. As further disclosed in Sawasaki et al., the pillar
spacers may be formed with different heights, such that some
spacers have a height that is greater than the gap between the
substrates and other spacers have a height that is less than the
gap between the substrates. This configuration may permit the
spacing between the substrates to vary with temperature changes but
also prevent excessive deformation when forces are applied to the
panel.
Sawasaki et al. further discloses a method for assembling the
substrates with the liquid crystal material between them. This
method comprises steps of preparing the two substrates, coating a
sealing material on the circumference of the outer periphery of one
of the pair of substrates, dropping an appropriate volume of liquid
crystal on one of the pair of substrates, and filling in the liquid
crystal between the pair of substrates by attaching the pair of
substrates in a vacuum followed by returning the attached pair of
substrates to atmospheric pressure.
In LCD panels, the semiconductor material making up the TFT channel
may be amorphous silicon. However, as disclosed in Chen, U.S. Pat.
No. 6,818,967, which is assigned to AU Optronics Corp., the parent
company of the assignee of the current application, and hereby
incorporated by reference in its entirety, poly-silicon channel
TFTs offer advantages over amorphous silicon TFTs, including lower
power and greater electron migration rates. Poly-silicon may be
formed by converting amorphous silicon to poly-silicon via a laser
crystallization or laser annealing technique. Use of the laser
permits fabrication to occur at temperatures below 600.degree. C.,
and the fabricating technique is thus called low temperature
poly-silicon (LTPS). As disclosed in Chen, the re-crystallization
process of LTPS results in the formation of mounds on the surface
of the poly-silicon layer, and these mounds impact the current
characteristics of the LTPS TFT. Chen discloses a method to reduce
the size of the LTPS surface mounds, by performing a first anneal
treatment, then performing a surface etching treatment, for example
using a solution of hydrofluoric acid, and then performing a second
anneal treatment. The resulting LTPS surface has mounds with a
height/width ratio of less than 0.2. A gate isolation layer, gate,
dielectric layer, and source and drain metal layers can then be
deposited above the LTPS layer to form a complete LTPS TFT.
As disclosed in Sun et al., U.S. Pat. No. 8,115,209, which is
assigned to AU Optronics Corp., the parent company of the assignee
of the current application, and hereby incorporated by reference in
its entirety, a disadvantage of LTPS TFTs compared to amorphous
silicon TFTs is a relatively large leakage current during TFT turn
off. Use of multiple gates reduces leakage current, and Sun et al.
discloses a number of different multi-gate structures for a
polycrystalline silicon TFT, including those shown in Sun et al.
FIGS. 2A-2B and 3-6.
As is well-known in the art, commonly-used liquid crystal molecules
exhibit dielectric anisotropy and conductive anisotropy. As a
result, the molecular orientation of liquid crystals can be shifted
under an external electric field. By varying the strength of the
external electric field, the brightness of the light that passes
through the polarizers and the liquid crystal material can be
controlled. By applying different electric fields within different
pixels of the array, and by providing different color filters for
different pixels, the brightness and color of the light passing
through each point in the LCD panel can be controlled, and a
desired image formed. Such LCDs employ a variety of liquid crystal
(LC) mixtures that have been developed to exhibit a range of
operating and performance characteristics.
For instance, polymer stabilized blue phase liquid crystal
(PS-BPLC) is attractive for use in displays due to some
revolutionary features, e.g., no need for an alignment layer, fast
response time, and an isotropic dark state. However, PS-BPLC
generally requires a high operation voltage because of its
relatively rigid polymer network.
From a materials perspective, large dielectric anisotropy
(.DELTA..epsilon.) LC mixtures (e.g., .DELTA..epsilon.>50) have
been developed and employed to generate a large Kerr constant, with
a correspondingly lower operation voltage. However, these LC
mixtures exhibit a long molecular conjugation length and large
dipole moment, resulting in a very high viscosity. Meanwhile, the
dielectric constant of BPLC host follows the Debye relaxation:
.DELTA..DELTA..infin..DELTA..DELTA..infin. ##EQU00001## in which
f.sub.r is the relaxation frequency and is related to the
rotational viscosity .eta. and molecule length l as:
.eta..times..times. ##EQU00002##
Due to the very high viscosity and long molecular length, the
relaxation frequency of high .DELTA..epsilon. BPLC host is quite
low. Unfortunately, such a low relaxation frequency may bring two
unwanted challenges: 1) insufficient charging time, and 2) high
temperature sensitivity. The challenge of insufficient charging
time may be addressed by some novel circuit designs, several of
which are disclosed in various publications, such as: C.-D. Tu, et
al. J. Display Technol. 9(1), 3 (2013); C.-L. Lin, et al. IEEE
Electron Device Letter, 36(4), 354 (2015); C.-L. Lin, et al. US
Patent Publication No. 2015/0262542 A1; and, C.-L. Lin, et al. US
Patent Publication No. 2015/0277177 A1, for example. However,
little progress has been achieved in addressing the issue of
temperature sensitivity.
As mentioned above, for a large-.DELTA..epsilon. BPLC, the Debye
relaxation frequency is as low as several kHz. Hence, the Kerr
constant strongly depends on the working temperature and driving
frequency [F. Peng, et al. J. Mater. Chem. C, 2, 3597 (2014)]:
.times..function..times..times..function..times. ##EQU00003## where
K is the Kerr constant, A is the proportionality constant, k.sub.B
is the Boltzmann constant, and T.sub.c is the clearing
temperature.
As can be seen from FIG. 1, the Kerr constant of a typical large
.DELTA..epsilon. BPLC host BP07 (.DELTA..epsilon..about.300)
decreases from 27.5 nm/V.sup.2 to 15 nm/V.sup.2, when the
temperature increases from 10.degree. C. to 30.degree. C. In such a
narrow temperature interval, the Kerr constant changes by
approximately a factor of two, and may lead to dysfunction of a
display in which the LC mixture is used.
Accordingly, there is a desire to reduce the temperature
sensitivity and widen the working temperature range of large
.DELTA..epsilon. LC mixtures, such as PS-BPLC.
SUMMARY
Liquid crystal display systems and related methods with pixel
elements driven at different frequencies are provided. In one
embodiment, a liquid crystal display (LCD) comprises: a plurality
of pixel elements arranged in an array, each of the plurality of
pixel elements having a first sub-region and a second sub-region; a
low-frequency driving circuit operative to drive each of the first
sub-regions; and a high-frequency driving circuit operative to
drive each of the second sub-regions at a driving frequency
different than a driving frequency of the low-frequency driving
circuits; wherein the first sub-regions exhibit a different size
than the second sub-regions.
In another embodiment, a method of driving an LCD comprises:
providing an LCD having a plurality of pixel elements arranged in
an array, and a plurality of driving circuits for driving the
plurality of pixel elements; driving a first sub-region of each of
the pixel elements at a first driving frequency; and driving a
second sub-region of each of the pixel elements at a second driving
frequency different than the first driving frequency; wherein the
first sub-regions exhibit a different size than the second
sub-regions.
In still another embodiment, an LCD system comprises: a pixel
element having a first sub-region and a second sub-region; a
low-frequency driving circuit disposed on the first sub-region; a
high-frequency driving circuit disposed on the second sub-region; a
plurality of date lines, with a first of the date lines being
coupled to the low-frequency driving circuit and a second of the
data lines being coupled to the high-frequency driving circuit; and
a plurality of gate lines, with a first of the gate lines being
coupled to the low-frequency driving circuit and a second of the
gate lines being coupled to the high-frequency driving circuit.
In yet another embodiment, a method of driving an LCD having a
plurality of pixel elements arranged in an array, comprises:
driving a first sub-region of each of the pixel elements, at a
first driving frequency, according to a first data signal
communicated by a first data line; and driving a second sub-region
of each of the pixel elements, at a second driving frequency
different than the first driving frequency, according to a second
data signal communicated by a second data line.
Other objects, features, and/or advantages will become apparent
from the following detailed description of the preferred but
non-limiting embodiments. The following description is made with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram illustrating temperature dependent Kerr
constants of a representative polymer stabilized blue phase liquid
crystal mixture (BP07) at different driving frequencies.
FIG. 2 is a schematic diagram of an embodiment of an LCD
system.
FIG. 3 is a schematic diagram of an embodiment of a pixel.
FIG. 4 is a schematic, side view of an embodiment of an LCD
system.
FIG. 5 is a diagram illustrating simulated temperature dependent
operation voltages for different driving frequencies (120Hz and
360Hz) and frequency combination (120Hz+360Hz) based on the
embodiment of FIG. 4.
FIG. 6 is a schematic, side view of another embodiment of an LCD
system.
FIG. 7 is a diagram illustrating simulated temperature dependent
operation voltages for different driving frequencies (120Hz and
360Hz) and frequency combination (120Hz+360Hz) based on the
embodiment of FIG. 6.
FIG. 8 is a flowchart illustrating basic operations in accordance
with an embodiment.
FIG. 9 is a schematic diagram of an embodiment of a pixel
element.
FIG. 10 is a flowchart illustrating basic operations in accordance
with another embodiment.
FIG. 11 is a signal diagram depicted representative gate control
and data signals that can be used in an example embodiment.
FIG. 12 is a schematic, side view of another embodiment of an LCD
system.
FIG. 13 is a diagram illustrating simulated temperature dependent
operation voltages for different driving frequencies (120Hz and
360Hz) and frequency combination (120Hz+360Hz) based on the
embodiment of FIG. 12.
DETAILED DESCRIPTION
For ease in explanation, the following discussion describes
embodiments of the present disclosure in the context of an LCD
system. It is to be understood that the invention is not limited in
its application to the details of the particular arrangements shown
since the invention is capable of other embodiments. Also, the
terminology used herein is for the purpose of description and not
of limitation.
In this regard, LCD systems and related methods with pixel elements
driven at different frequencies are provided. As will be described
in greater detail below, such systems and methods may involve the
use of large .DELTA..epsilon. LC materials (e.g., PS-BPLCD) that
exhibit reduced temperature sensitivity. The preferred embodiments
of the present invention will now be described with reference to
the drawings.
With reference to FIG. 2, an embodiment of an LCD system 100 is
depicted. Fundamentally, LCD system 100 includes an LCD panel 110
with a plurality of pixels, data control circuitry 120 and gate
control circuitry 130. The circuits and functions in the
embodiments of the present invention can be implements by hardware,
software or a combination of hardware and software such as
microcontrollers, application-specific integrated circuits (ASIC)
and programmable microcontrollers.
In keeping with the description of FIG. 2, LCD panel 110
incorporates a plurality of pixels (typically thousands of pixels,
e.g., pixels 140, 150), which are arranged in a two-dimensional
array comprising a plurality of rows and columns. For ease in
illustration, only a few pixels are illustrated in FIG. 2. As is
known, in a thin film transistor (TFT) LCD panel, a pixel is
typically formed from three pixel elements (PEs): one red, one
green, and one blue, although various configurations may be used.
For instance, pixel 150 is depicted as including three PEs--PE(R),
PE(G) and PE(B). One or more transistors and one or more storage
capacitors are typically coupled to each pixel element, thereby
forming driving circuitry for the associated pixel element.
The transistors of all pixels in a given row typically have their
gate electrodes connected to a gate line (e.g., line 152), and
their source electrodes connected to a data line (e.g., line 154).
The gate control circuitry 130 and data control circuitry 120
control the voltage applied to the respective gate and data lines
to individually address each pixel element in the LCD panel. By
controllably pulsing the respective pixel element driving
transistors, the driving circuits can control the transmissivity of
each PE, and thereby control the color of each pixel. The storage
capacitors assist in maintaining the charge across each pixel
between successive pulses (which are delivered in successive
frames).
An embodiment of a pixel 150 that may be implemented in an LCD
system (such as LCD system 100 of FIG. 1) is depicted schematically
in FIG. 3. As shown in FIG. 3, pixel 150 incorporates three PEs--a
red PE, a green PE and a blue PE, denoted by PE(R), PE(G) and
PE(B), respectively. Each of the PEs is divided into two
sub-regions that share the structural components of a PE (e.g., a
corresponding color filter). Additionally, each sub-region is
associated with a dedicated driving circuit. Specifically, PE(R)
includes sub-regions 162, 164, PE(G) includes sub-regions 172, 174,
and PE(B) includes sub-regions 182, 184. The sub-regions 162, 164,
172, 174, 182 and 184 are associated with driving circuits 163,
165, 173, 175, 183 and 185, respectively. Notably, driving circuits
163, 173 and 183 operate at a different driving frequency (f.sub.1)
than the driving frequency (f.sub.2) of driving circuits 165, 175
and 185.
In some embodiments, driving circuits 163, 173 and 183 can be
configured as low-frequency driving circuits for operating at a
driving frequency lower than the driving frequency of driving
circuits 165, 175 and 185 (thus, becoming high-frequency driving
circuits). By way of example, the low-frequency driving circuits
are driven at 120Hz and the high-frequency driving circuits are
driven at 360Hz. Preferably, the driving frequencies of the driving
circuits are in the range of approximately 60Hz to approximately
480Hz. Other frequencies also are applicable (e.g., 1200Hz),
however, such frequencies may introduce issues (e.g., charging
issues). Additionally, the driving frequency of the high-frequency
driving circuits is preferably a multiple of the driving frequency
of the low-frequency driving circuits (e.g., 120Hz*3=360Hz).
Each of sub-regions 162, 172 and 182 (although similar in size with
respect to each other) are different in size than the sub-regions
164, 174 and 184. In this embodiment, sub-regions 162, 172 and 182
are smaller in size (i.e., correspond to a smaller area when viewed
in plan view) than sub-regions 164, 174 and 184. Preferably, the
ratio of the areas of the sub-regions for a PE is in the range of 1
to approximately 10, although other ratios may be used. For
example, the ratio of the area of the sub-region 162 to the
sub-region 164 is 1:2 and as a result the area of the sub-region
162 is smaller than the sub-region 164. In another case, the ratio
of the area of the sub-region 162 to the sub-region 164 is 0.1:1
and as a result the area of the sub-region 162 is bigger than the
sub-region 164. In other case, the ratio of the area of the
sub-region 162 to the sub-region 164 is 1:1 and as a result the
area of the sub-region 162 is equal to the sub-region 164. In some
embodiments, the size of the larger sub-regions is at least
approximately 2 times the size of the smaller sub-regions. It
should be noted that the selection of sub-region sizes (as with
driving frequency) may be based on a variety of factors such as LC
materials, electrode structures, and required working temperature
range, among others.
In the embodiment of FIG. 3, the smaller sub-regions 162, 172 and
182 are driven by the associated driving circuits at lower driving
frequencies than the frequencies used for driving the larger
sub-regions 164, 174 and 184. In other embodiments, the smaller
sub-regions are driven at higher driving frequencies than the
frequencies used for driving the larger sub-regions. In such an
embodiment, however, the working temperature range will likely be
influenced more by low frequency driving since the area of the
sub-regions driven by the low-frequency driving circuits would be
larger than that driven by the high-frequency driving circuits.
FIG. 4 is a schematic, side view of an embodiment of an LCD system
200 that includes sub-regions 202 and 204, with the sub-regions
being operated at different driving frequencies. In particular,
sub-region 202 is driven at high frequency (HF) and sub-region 204
is driven at low frequency (LF).
As shown in FIG. 4, LCD system 200 is configured as an in-plane
switching (IPS) LCD panel that incorporates an upper substrate 210,
a lower substrate 212 and a large .DELTA..epsilon. LC mixture 214
sandwiched between the substrates. It should be noted that for
TFT-grade nematic LCs, dielectric anisotropy is usually
.DELTA..epsilon.<10 in order to obtain low viscosity. However,
for blue phase LCDs, in order to reduce operation voltage, an LC
host with .DELTA..English Pound.>50 is often chosen--a large
.DELTA..epsilon. LC mixture. Some commercially available blue phase
LC hosts exhibit .DELTA..epsilon.>100.
LC mixture 214 includes liquid crystal molecules that exhibit
optical isotropicity. In this embodiment, the liquid crystal
molecules are BPLC, with BP07 (.DELTA..epsilon..about.300) being
used as the BP host. However, in other embodiments, various other
large .DELTA..epsilon. LC mixtures may be used, such as uniformly
standing helix LCs, uniformly lying helix LCs or other LC modes,
for example.
Sub-regions 202 and 204 exhibit equal lengths (l.sub.1=l.sub.2),
with the electrodes being formed on lower substrate 212. The
electrodes (e.g., electrodes 221, 222, 223 and 224) exhibit the
same width/gap and the same height. For example, the width/gap is
3.mu.m/10.mu.m and the protrusion height is 3.5 .mu.m. It should be
noted that, in other embodiments, various other electrode
configurations may be used, such as fringe-field switching (FFS)
and vertical field switching (VFS), for example.
To reduce the temperature sensitivity of Kerr constant, pixels of
sub-region 202 are operated at a higher driving frequency (or frame
rate) than the driving frequency of pixels of sub-region 204. Since
the optimal temperature (T.sub.op) with highest Kerr constant is
different for each frequency (e.g., 8.degree. C. for 120Hz and
18.degree. C. for 360Hz), by combining sub-regions 202 and 204, the
pixels of the LCD panel exhibit wider working temperature
ranges.
FIG. 5 illustrates simulated temperature dependent operation
voltages for different driving frequencies (120Hz and 360Hz) and
frequency combination (120Hz+360Hz) based on the embodiment of FIG.
4. As shown in FIG. 5, for single frequency driving (e.g. 120Hz or
360Hz), the temperature range (V.sub.op+1.0 V) is about 10.degree.
C., which is much narrow for regular usage. But when dual frame
rates are employed, the temperature range nearly doubles, including
the room temperature. Moreover, the device parameters (e.g., areas
of sub-pixels, electrode structures, protrusion height of
electrodes, etc.) could be optimized to further enlarge the
temperature range. Also, if higher driving frequency is acceptable,
then better performance could be obtained.
FIG. 6 is a schematic, side view of another embodiment of an LCD
system 250 configured as an IPS LCD panel that incorporates an
upper substrate 260, a lower substrate 262 and a large
.DELTA..epsilon. LC mixture 264 (e.g., BP07) sandwiched between the
substrates. As shown in FIG. 6, the LCD system 250 is divided into
two sub-regions 252 and 254, with sub-region 252 (HF sub-region)
being operated at a higher driving frequency than the driving
frequency of sub-region 254 (LF sub-region).
Sub-regions 252 and 254 exhibit different lengths
(l.sub.1.noteq.l.sub.2, and l.sub.1:l.sub.2=4:1) and different
electrode configurations. In particular, the electrodes are formed
on lower substrate 262, with electrodes of sub-region 252 (e.g.,
electrodes 271, 272) exhibiting a width/gap of 3.mu.m/10.mu.m, and
electrodes of sub-region 254 (e.g., electrodes 281, 282) exhibiting
a width/gap of 3.mu.m/8.5.mu.m. Height of the electrodes is 3.5
.mu.m for both sub-regions.
FIG. 7 illustrates simulated temperature dependent operation
voltages for different driving frequencies (120Hz and 360Hz) and
frequency combination (120Hz+360Hz) based on the embodiment of FIG.
6. As can be seen, the optimal temperature range is widened
compared to that shown in FIG. 5. Potentially more significantly,
the range is shifted to high temperature, where room temperature
(22.degree. C.) is centered. As such, this performance may be more
preferable for commercial applications.
FIG. 8 is a flowchart illustrating basic operations in accordance
with an embodiment. As shown in FIG. 8, the functionality (or
method) associated with driving an LCD is construed as beginning at
block 300, in which an LCD is provided. In particular, the LCD
includes a plurality of pixel elements arranged in an array having
a plurality of column and a plurality of rows, and a plurality of
driving circuits for driving the plurality of pixel elements. In
some embodiments, each of the plurality of pixel elements is
associated with two driving circuits. An example embodiment of a
pixel element with two driving circuits will be described in detail
with respect to FIG. 9.
In block 302, a first sub-region of each of the pixel elements is
driven at a first driving frequency, such as is performed by a
first driving circuit. In block 304, a second sub-region of each of
the pixel elements is driven at a second driving frequency
different than the first driving frequency. This is performed by a
second driving circuit. Notably, the first sub-region of each of
the pixel elements exhibits the first size and the second
sub-region of each of the pixel elements exhibits the second size
different than the first size. Thus, in some embodiments, the
larger sub-regions are driven at higher frequencies than the
driving frequencies of the smaller sub-regions while, in other
embodiments, the larger sub-regions are driven at lower frequencies
than the smaller sub-regions.
FIG. 9 is a schematic diagram of an embodiment of a pixel element
(PE) 310 that incorporates an LF sub-region 311 and an HF
sub-region 331 associated with LF driving circuit 312 and HF
driving circuit 332, respectively. LF driving circuit 312 includes
a switch 314, a storage capacitor (C.sub.ST) 316 and a liquid
crystal capacitor (C.sub.LC) 318. Switch 314 includes a first
terminal 320, a second terminal 322 and a gate terminal 324. The
first terminal 320 is coupled to a first data line 326 for
receiving a first data signal. The capacitors 316 and 318 are
coupled in parallel to the second terminal 322. The gate terminal
324 is coupled to a first gate line 328 for receiving a first gate
control signal.
HF driving circuit 332 includes a switch 334, a storage capacitor
(C.sub.ST) 336 and a liquid crystal capacitor (C.sub.LC) 338.
Switch 334 includes a first terminal 340, a second terminal 342 and
a gate terminal 344. The first terminal 340 is coupled to a second
data line 346 for receiving a second data signal. The capacitors
336 and 338 are coupled in parallel to the second terminal 342. The
gate terminal 344 is coupled to a second gate line 348 for
receiving a second gate control signal.
In this embodiment, the switches 314 and 334 are transistors (e.g.,
TFTs) that are turned on when the respective gate terminals receive
an enabling signal. The liquid crystal capacitors 318 and 338 are
formed by BPLC, for example.
In operation, LF driving circuit 312 and HF driving circuit 332 are
driven a different frequencies (e.g., 120HZ and 360Hz,
respectively). Specifically, gate lines 328, 348 are pulsed at
corresponding driving frequencies to enable respective gate
terminals 324 and 344. By pulsing the driving switches 314 and 334
at the corresponding frequencies, the driving circuits 312 and 332
control the transmissivity of associated sub-regions of PE 310 in
accordance with data signals provided by data lines 326 and 346. As
such, the LC mixture used in the PE exhibits reduced temperature
sensitivity and a widened working temperature range.
It should be noted that the use of two data lines per PE (such as
depicted in FIG. 9) may be preferable in some embodiments.
Specifically, TFTs are typically AC-driven, which presents the
potential for sub-region to sub-region crosstalk as the polarity of
the voltage applied to a sub-region may be inverted with respect to
another sub-region. Use of the independent data lines for each
sub-region of a PE may alleviate this issue.
It should also be noted that, although each of the driving circuits
of the embodiment of FIG. 9 is a standard one transistor and two
capacitor (1T2C) circuit, other circuit configurations (such as
modified 1T2C TFT, 2T3C TFT, and 4T2C TFT, among others) may be
used in other embodiments.
FIG. 10 is a flowchart illustrating basic operations in accordance
with another embodiment, such as the embodiment depicted in FIG. 9.
As shown in FIG. 10, the functionality (or method) associated with
driving an LCD is construed as beginning at block 350, in which an
LCD having a plurality of pixel elements arranged in an array is
provided. In block 352, a first sub-region of each of the pixel
elements is driven, at a first driving frequency, according to a
first data signal communicated by a first data line.
By way of example, the diagram of FIG. 11 depicts representative
signals that may be used. In particular, FIG. 11 shows a first data
signal (Data-1) and a corresponding first gate control signal
(Gate-1), as well as a second data signal (Data-2) and a
corresponding second gate control signal (Gate-2). In operation,
with respect to the functionality of block 352, the first gate
control signal pulses a driving switch associated with the first
sub-region to control the transmissivity of the first sub-region in
accordance with the first data signal.
In block 354, a second sub-region of each of the pixel elements is
driven, at a second driving frequency different than the first
driving frequency, according to a second data signal communicated
by a second data line. For instance, the second gate control signal
(Gate-2) is used to pulse a driving switch associated with the
second sub-region to control the transmissivity of the second
sub-region in accordance with the second data signal (Data-2). Note
that, in the embodiment of FIG. 11, the second driving frequency is
higher than the first driving frequency.
FIG. 12 is a schematic, side view of another embodiment of an LCD
system 400 configured as LCD panel that incorporates an upper
substrate 410, a lower substrate 412 and a large .DELTA..epsilon.
LC mixture 414 (e.g., BP07) sandwiched between the substrates. As
shown in FIG. 12, the LCD system 400 is divided into two
sub-regions 422 and 424, with sub-region 422 (HF sub-region) being
operated at a higher driving frequency than the driving frequency
of sub-region 424 (LF sub-region).
In this embodiment, first pixel elements 430 and corresponding
pixel electrodes (e.g., electrode 431) are disposed on upper
substrate 410, and second pixel elements 432 and corresponding
pixel electrodes (e.g., electrode 433) are disposed on lower
substrate 412.
Simulated temperature dependent operation voltages for different
driving frequencies (120Hz and 360Hz) and frequency combination
(120Hz+360Hz) based on the embodiment of FIG. 12 are illustrated in
the graph of FIG. 13. Since the light goes through the LF and HF
regions (lower and upper) separately and consecutively, the
effective Kerr constant would be the sum of these two layers, which
means:
.DELTA.n.sub.ind=.DELTA.n.sub.ind-1+.DELTA.n.sub.ind-2=.lamda.(K.sub.1+K.-
sub.2)E.sup.2. (4)
Therefore, apart from the wider temperature range, the operation
voltage is decreased (<15V) for this embodiment. As is shown,
low operation voltage is good for charging, meanwhile voltage less
than 15V enables one thin-film transistor (TFT) driving on each
substrate. Thus, low cost and ease of driving may be achieved.
The embodiments described above are illustrative of the invention
and it will be appreciated that various permutations of these
embodiments may be implemented consistent with the scope and spirit
of the invention.
* * * * *